public static double[] FFTWPaddedFFT(ref double[] @in)
{
Debug.Assert(@in.Length > 0);
int n = @in.Length;
int padded = n > 256 ? MathUtils.NextLowPrimeFactorization(n) : n;
Array.Resize <double>(ref @in, padded);
// 4096 real numbers on input processed by FFTW dft_r2c_1d transform gives
// 4096/2+1 = 2049 complex numbers at output
// prepare the input arrays
var fftwInput = new FFTW.DoubleArray(@in);
int complexSize = (padded >> 1) + 1; // this is the same as (padded / 2 + 1);
var fftwOutput = new FFTW.ComplexArray(complexSize);
FFTW.ForwardTransform(fftwInput, fftwOutput);
Array.Resize <double>(ref @in, n);
// free up memory
GC.Collect();
return(fftwOutput.ComplexValues);
}
public static void ForwardTransform(FFTW.DoubleArray input, FFTW.ComplexArray output)
{
IntPtr plan = FFTW.dft_r2c_1d(input.Length, input.Handle, output.Handle, Flags.Estimate);
//FFTW.print_plan(plan);
FFTW.execute(plan);
FFTW.destroy_plan(plan);
}
public static void BackwardTransform(FFTW.ComplexArray input, FFTW.DoubleArray output)
{
// TODO: will there be a time where input.Length should be used instead?
IntPtr plan = FFTW.dft_c2r_1d(output.Length, input.Handle, output.Handle, Flags.Estimate);
//FFTW.print_plan(plan);
FFTW.execute(plan);
FFTW.destroy_plan(plan);
}
public static double[] FFTWPaddedIFFT(ref double[] @in, bool doProperScaling = true)
{
Debug.Assert(@in.Length > 1);
int originalLength = @in.Length;
int n = @in.Length - 2;
// the complex array should in theory always be correct size?
// int padded = n > 256 ? MathUtils.NextLowPrimeFactorization(n) : n;
int padded = n;
//Array.Resize<double>(ref @in, padded);
// prepare the input arrays
var fftwBackwardInput = new FFTW.ComplexArray(@in);
var fftwBackwardOutput = new FFTW.DoubleArray(padded);
// this method needs that the backwards transform uses the output.length as it's N
// i.e. FFTW.dft_c2r_1d(output.Length, input.Handle, output.Handle, Flags.Estimate);
FFTW.BackwardTransform(fftwBackwardInput, fftwBackwardOutput);
double[] @out = null;
if (doProperScaling)
{
@out = fftwBackwardOutput.ValuesDivedByN;
}
else
{
// in the original method it wasn't scaled correctly (meaning ValuesDivedByN)
@out = fftwBackwardOutput.Values;
}
//Array.Resize<double>(ref @in, originalLength);
// free up memory
GC.Collect();
return(@out);
}
